The overall objective of this proposal is to determine if potassium-magnesium citrate (K-Mag) could prevent bone loss in postmenopausal women, and if it does so, to ascertain the mechanism for this action and contrast it from that of calcium citrate. The project will test the hypothesis that K-Mag would avert bone loss in postmenopausal women by a direct action of alkali on osteoclastic resorption and osteoblastic formation, unlike calcium citrate which inhibits bone loss by suppressing parathyroid hormone secretion.